In the process of manufacturing metallic sheet material, such as steel sheets, titanium sheets, and aluminum sheets, the sheet material is subjected to rolling and cooling steps, in which deformation, such as warping and/or waving, occurs in the sheet material. In order to eliminate the deformation, such as warping and/or waving, and thereby to flatten the sheet material, a roller leveler, which includes a plurality of leveling rolls disposed on upper and lower sides in a staggered manner, is used (see Patent Document 1, for example).
In the roller leveler, sheet material to be flattened is passed through the roller leveler, with the upper leveling rolls being pressed toward the lower leveling rolls or the lower leveling rolls being pressed toward the upper leveling rolls, to repeatedly bend the sheet material, and thereby to planarize the warping and/or waving of the sheet material.
In such a roller leveler, the leveling range, in which the sheet material can be flattened by the roller leveler, is limited and therefore, in order to sufficiently flatten the sheet material having the maximum thickness within the requirement range, large-diameter leveling rolls that are strong enough to ensure safety are used and the roll pitch is correspondingly set. A roller leveler for thin sheets (thickness is about 6 mm or below) uses leveling rolls with a diameter of 70 mm, of which the roll pitch is 105 mm, for example.
When a thinner sheet material is leveled or flattened, a tension leveler is used that performs flattening of a continuous sheet material with the use of leveling rolls while applying tensile force to the continuous sheet material (see Patent Document 2, for example). The tension leveler repeatedly bends the sheet material with the use of small-diameter leveling rolls while applying tensile force to the sheet material, thereby planarizing the warping and/or waving of the sheet material.